Lung function tests (spirometry and peak expiratory flow[PEF]) are normal when the person is not having an asthma attack. The results of these tests are 80% or more of the expected value and vary little (PEF varies less than 20%) from morning to afternoon.

Mild persistent asthma

Asthma is considered mild persistent if without treatment any of the following are true:

Symptoms occur on more than 2 days a week but do not occur every day.

Attacks interfere with daily activities.

Nighttime symptoms occur 3 to 4 times a month.

Lung function tests are normal when the person is not having an asthma attack. The results of these tests are 80% or more of the expected value and may vary a small amount (PEF varies 20% to 30%) from morning to afternoon.

Moderate persistent asthma

Asthma is considered moderate persistent if without treatment any of the following are true:

Nighttime symptoms occur more than 1 time a week, but do not happen every day.

Lung function tests are abnormal (more than 60% to less than 80% of the expected value), and PEF varies more than 30% from morning to afternoon.

Severe persistent asthma

Asthma is considered severe persistent if without treatment any of the following are true:

Symptoms:

Occur throughout each day.

Severely limit daily physical activities.

Nighttime symptoms occur often, sometimes every night.

Lung function tests are abnormal (60% or less of expected value), and PEF varies more than 30% from morning to afternoon.

If you or your child has persistent asthma (mild, moderate, or severe) and is receiving appropriate therapy, the goal of treatment should be to control symptoms so that they occur only as frequently as those of intermittent asthma.

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